修改 隐藏和显示 NavigationBar方法。

主要是为了让过度动画更加自然，现在版本从照片列表到预览界面导航栏会有变白的过渡。

TZImagePickerController/TZImagePickerController/TZPhotoPreviewController.m

@@ -56,7 +56,7 @@
 
 - (void)viewWillAppear:(BOOL)animated {
     [super viewWillAppear:animated];
-    [self.navigationController setNavigationBarHidden:YES];
+    [self.navigationController setNavigationBarHidden:YES animated:YES];
     if (iOS7Later) [UIApplication sharedApplication].statusBarHidden = YES;
     if (_currentIndex) [_collectionView setContentOffset:CGPointMake((self.view.tz_width + 20) * _currentIndex, 0) animated:NO];
     [self refreshNaviBarAndBottomBarState];
@@ -64,7 +64,7 @@
 
 - (void)viewWillDisappear:(BOOL)animated {
     [super viewWillDisappear:animated];
-    [self.navigationController setNavigationBarHidden:NO];
+    [self.navigationController setNavigationBarHidden:NO animated:YES];
     if (iOS7Later) [UIApplication sharedApplication].statusBarHidden = NO;
 }